Magnets have been used to act as dampeners such as in the context of exercise equipment as illustrated in U.S. Pat. No. 5,752,879. Magnets have been used in fluid flow systems to hold a position of a moving component such as for example in an open or a closed position. Illustrative of a gas line and a medical device application are U.S. Pat. No. 5,209,454 and U.S. Pat. No. 5,970,801. In a similar vein is U.S. Pat. No. 7,527,069. The use of magnets to control the fixation of a movable member in a level control application is seen in U.S. Pat. No. 4,436,109. These disparate applications seek to use the force of a magnetic field for fixation to a given position. Some of them release the component when the magnetic field is deactivated.
In downhole applications and most particularly in valves where large pressure differentials can build in an instant as a valve member such as a flapper moves against a seat, there can be serious damage from the impact force that can be severe enough to deform the valve member or the mating seat. In the case of subsurface safety valve flappers, when opened but more so when allowed to close, there is a risk of flapper or seat damage or damage to both from a severe impact loading. Accordingly the present invention seeks to cushion or even eliminate the shock contact while still allowing the movable member to reach its intended ultimate position. In the context of a flapper, the preferred embodiment locates at least one magnet on the flapper and magnets in the housing adjacent the location of the flapper when it reaches its ultimate open or closed position. In this manner the application of a magnetic field to the pivoting flapper damps any impact with the seat in the closed position and any travel stop for the open position. These and other features of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated FIGS. while recognizing that the full scope of the invention is given by the appended claims.